1. Field of the Invention
The present invention relates to sensing of torque in a drive system of a processor of photosensitive material.
2. Description of the Prior Art
In photofinishing, it is typical to continuously process long webs of photosensitive material by transporting the web through a series of processing tanks which contain different chemical solutions, and then through a dryer that dries the web. Both photographic film and photographic print paper are commonly processed in this manner.
In the case of photographic film, it is typical to splice together individual strips of undeveloped photographic film for processing. Cine processor machines are used to develop continuously a long web of photographic film formed by splicing together individual strips of film.
In a cine processor, the film web is transported through the tank by sets of transport rollers. Typically, each tank has a transport rack with an upper and lower shaft on which are mounted a plurality of transport rollers. The lower shafts on which the transport rollers are mounted are driven through a gear train by the cine processor drive system. The film web enters a transport rack on one side, and is transported in a helical manner between the upper and lower rollers of the rack until it reaches the outside of the rack where it is transferred to the next transport rack.
As is easily apparent, any malfunction in the processor drive system results in costly down time and possible damage to the photosensitive web. An important component of the drive system is the gears that transfer the power from a main drive shaft to the transport rollers of appropriate shafts of the transport rack. Typically, there is a lower pair of cooperating gears that are submerged in the tank solution and an upper gear not in the tank solution cooperating with a main drive shaft gear. These gears are often made of plastic since they have to be resistant to chemical attack from the various chemical solutions used in the processor.
The main drive shaft gear which transfers power from the main drive shaft to the plastic gears cannot be made of a similar plastic as analogous plastics tend to adhere under load, causing accelerated wear and binding. Typically, the gears on the main drive shaft are made of stainless steel to avoid such binding. However, both cooperating gears that are completely submerged in the solution are made of plastic and do not bind since the solution acts as a buffer.
As the cine processor is used over a considerable amount of time, torque tends to develop in the drive system to a point where the weaker components, such as the plastic gears, are endangered. The torque develops from several sources. First, the bearings in the transport rollers tend to wear out. Second, the web from time to time wraps around the elements in the tank during a break. Third, many of the parts of the transport rack are made of plastic and may tend to swell and bind after considerable time in the various tank solutions causing torque to develop. If the torque problem is not corrected in time, a breakdown of the processor drive system will occur resulting in costly downtime and maintenance.